Rh Factor

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Rh factor

Rh factor is a protein called an antigen that is found on the red blood cells of most people. (An antigen is any substance that the body considers "foreign" and thus stimulates the body to produce antibodies against it.) Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85 percent of white Americans and 95 percent of African Americans have the Rh factor and are known as Rh-positive. Those without the Rh factor are Rh-negative.

Rh factor in pregnancy

Rh factor plays a critical role in some pregnancies. If a woman who is Rh-negative becomes pregnant by a man who is Rh-positive, the fetus may inherit the Rh factor from its father and be Rh-positive. If the blood of the fetus becomes mixed with the mother's Rh-negative blood, a disease called erythroblastosis fetalis can occur in future pregnancies, resulting in destruction of the fetus's red blood cells, brain damage, and even death.

The mixing of blood does not normally occur but may take place before or during birth if a tear in the placenta (the organ through which nutrients pass from the mother to the fetus) allows some fetal blood to enter the mother's circulatory system. If this happens, the fetus's red blood cells bearing the Rh factor stimulate the mother's white blood cells to produce antibodies against the foreign antigen. The mother's blood is now sensitized to the Rh factor.

Once a mother's blood is sensitized, the antibodies her body produces in response to the Rh antigen can cross the placenta and attach to the red blood cells of any Rh-positive fetus that she carries. This results in the rupture of the fetus's red blood cells, causing anemia (a condition marked by weakness and fatigue due to a reduced number of red blood cells). Severe anemia can lead to heart failure and death. The breakdown of red blood cells also causes the overproduction of a reddish-yellow substance called bilirubin. An infant with high levels of bilirubin will develop jaundice (have a yellowish appearance) and may suffer brain damage.

Prevention of erythroblastosis fetalis

Erythroblastosis fetalis can be prevented by administering a preparation of anti-Rh factor antibodies to an Rh-negative mother whose blood has not yet produced antibodies to the Rh antigen. The preparation, known as Rh immune globulin, rids the mother's blood of fetal red blood cells before she can become sensitized to them. Rh immune globulin is given whenever there is a possibility of fetal blood mixing with maternal blood, such as following childbirth, an abortion, a miscarriage, or prenatal testing.

Treatment for erythroblastosis fetalis

Treatment for erythroblastosis fetalis depends to what extent the fetus is affected by the action of its mother's anti-Rh-factor antibodies. A fetus whose red blood cells are being severely destroyed can be treated

with transfusions (replacement) of Rh-negative blood while it is still in the uterus. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early. The baby's blood is then replaced with Rh-negative blood following birth.

A pregnant woman who is already sensitized to the Rh antigen can have her doctor carefully monitor the level of antibodies in her blood throughout her pregnancy. If the levels rise, the fetus will need special attention. Unfortunately, once a woman is sensitized, she will always produce antibodies when exposed to the Rh antigen.

Words to Know

Antibody: A protein produced by certain cells of the body as an immune (disease-fighting) response to a specific foreign antigen.

Antigen: Any substance that the body considers foreign and that stimulates the body to produce antibodies against it.

Bilirubin: Reddish-yellow substance produced by the breakdown of red blood cells.

Erythroblastosis fetalis: A disease of fetuses and newborns caused by the mixing of fetal Rh-positive blood with maternal Rh-negative blood and resulting in rupture of fetal red blood cells.

Placenta: The organ formed during pregnancy in mammals through which substances are exchanged between mother and fetus.

Protein: Large molecules that are essential to the structure and functioning of all living cells.

Sensitization: The initial exposure to a specific antigen that causes an immune reaction in the body.

[See alsoAntibody and antigen; Blood ]

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Rh Factor

Medical Discoveries
COPYRIGHT 1997 Thomson Gale

Rh factor

Rh factor is also called "Rhesus factor" because it was first discovered in the blood of Rhesus monkeys (small monkeys from India often used for experimentation). Rh factor is an antigen, a substance which stimulates the production of antibodies to fight foreign invaders, such as viruses, bacteria and transplanted organs. A given individual either has the antigen already in their blood (they are Rh positive), or they don't (they are Rh negative). A patient's Rh status effects how he or she handles blood transfusions or organ transplants.

History

Prior to the twentieth century, blood and its function was poorly understood. In trying to solve the problem of serious blood loss from
injuries, doctors tried to inject (transfuse) blood from another person or animal into the injured patient. In some cases, this worked and the patient recovered. In many more cases, however, the blood transfusion actually harmed the patient, often causing death. No one could predict which type of reaction would occur as a result of a blood transfusion. So, by the beginning of the nineteenth century, most European nations had outlawed the practice of blood transfusion.

About 1900 Austrian-American physician Karl Landsteiner (1868-1943) developed an explanation for the phenomenon of blood rejection. Landsteiner found that human blood serum (the liquid portion of blood surrounding the cells) could be divided into four categories, depending on its ability to cause clotting of red blood cells. He gave these groups the names A, B, AB, and 0 based on what type of clotting antigen they had, if any.

In 1940 Landsteiner discovered another of blood factor antigen, known as Rh. This discovery resulted from Landsteiner's studies with Rhesus monkeys. Landsteiner and his colleagues found that when blood from monkeys was injected into rabbits and guinea pigs, it clotted. This was because of the presence of another antigen that the researchers had not classified before. Landsteiner called this antigen the Rh (Rhesus) factor. Researchers also showed that the factor occurs among some, but not all, humans. It is also inherited.

Importance of Rh Factor

The Rh discovery had immediate practical importance because it explained a relatively common medical disorder known as erythroblastosis fetalis. In this condition, an Rh-negative woman who becomes pregnant with an Rh-positive fetus (an unborn child) sometimes develops anti-bodies against the Rh factor in the fetus. This development usually causes no problem during the woman's first pregnancy, since the number of anti-bodies produced tends to be small.

By the time a second pregnancy occurs, the situation has changed. The number of Rh antibodies produced by the mother's body has become large enough to cause destruction of red blood cells in the fetus. This can result in complications such as anemia (a chronic blood condition characterized by lack of energy), jaundice (a condition in which bile pigments build up in the blood and cause skin, eyeballs and urine to take on a sickly yellow tone) or premature birth. Today, this reaction can be controlled by immunizing Rh negative women after their first pregnancy with a drug known as RhoGam.

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Rh factor

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

Rh factor, protein substance present in the red blood cells of most people, capable of inducing intense antigenic reactions. The Rh, or rhesus, factor was discovered in 1940 by K. Landsteiner and A. S. Wiener, when they observed that an injection of blood from a rhesus monkey into rabbits caused an antigenic reaction in the serum component of rabbit blood (see immunity). When blood from humans was tested with the rabbit serum, the red blood cells of 85% of the humans tested agglutinated (clumped together). The red blood cells of the 85% (later found to be 85% of the white population and a larger percentage of blacks and Asians) contained the same factor present in rhesus monkey blood; such blood was typed Rh positive. The blood of the remaining 15% lacked the factor and was typed Rh negative. Under ordinary circumstances, the presence or lack of the Rh factor has no bearing on life or health. It is only when the two blood types are mingled in an Rh-negative individual that the difficulty arises, since the Rh factor acts as an antigen in Rh-negative persons, causing the production of antibodies. Besides the Rh factor, human red blood cells contain a large number of additional antigenic substances that have been classified into many blood group systems (see blood groups); however, the Rh system is the only one, aside from the ABO system, that is of major importance in blood transfusions. If Rh-positive blood is transfused into an Rh-negative person, the latter will gradually develop antibodies called anti-Rh agglutinins, that attach to the Rh-positive red blood cells, causing them to agglutinate. Destruction of the cells (hemolysis) eventually results. If the Rh-negative recipient is given additional transfusions of Rh-positive blood, the concentration of anti-Rh agglutinins may become high enough to cause a serious or fatal reaction. The same type of immune reaction occurs in the blood of an Rh-negative mother who is carrying an Rh-positive fetus. (The probability of this situation occurring is high if the father is Rh positive.) Some of the infant's blood may enter the maternal circulation, causing the formation of agglutinins against the fetal red blood cells. The first baby is usually not harmed. But, if the mother's agglutinins pass into the circulation of subsequent fetuses, they may destroy the fetal red blood cells, causing the severe hemolytic disease of newborns known as erythroblastosis fetalis.

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rhesus factor

rhesus factor (Rh factor) An antigen whose presence or absence on the surface of red blood cells forms the basis of the rhesus blood group system. (The factor was first recognized in rhesus monkeys.) Most people possess the Rh factor, i.e. they are rhesus positive (Rh+). People who lack the factor are Rh–. If Rh+ blood is given to an Rh– patient, the latter develops anti-Rh antibodies. Subsequent transfusion of Rh+ blood results in agglutination, with serious consequences. Similarly, an Rh– pregnant woman carrying an Rh+ fetus may develop anti-Rh antibodies in her blood; these will react with the blood of a subsequent Rh+ fetus, causing anaemia in the newborn baby.

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rhesus factor

rhesus factor (Rh factor) (ree-sŭs) n. a group of antigens that may or may not be present on the surface of the red blood cells; it forms the basis of the rhesus blood group system. Most people have the rhesus factor, i.e. they are Rh-positive. People who lack the factor are termed Rh-negative. Incompatibility between Rh-positive and Rh-negative blood is an important cause of blood transfusion reactions and of haemolytic disease of the newborn. See also blood group. www.blood.co.uk/pages/e13basic.html Explanation of the Rh factor from the National Blood Service

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rhesus factor

rhesus factor (Rh factor) An antigen that occurs on the surface of the red blood cells of some individuals (who are designated rhesus positive, Rh positive, or Rh+) but not of others (who are rhesus negative, Rh negative, or Rh–). An Rh– person will develop anti-Rh antibodies when given Rh+ blood; a subsequent transfusion of Rh+ blood will then cause agglutination. The phenomenon was first detected in rhesus monkeys (see CERCOPITHECIDAE).

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rhesus factor

rhesus factor (Rh factor) Any of a group of antigens found on the surface of erythrocytes (red blood cells). Rh-negative (Rh−) blood lacks the rhesus factor. Rh factor is present in c.85% of humans (Rh+). Rh incompatibility (an Rh− pregnant woman with an Rh+ fetus) can give rise to anaemia in newborn babies. The antigens were first identified in the blood of rhesus monkeys.

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Rhesus factor

Rhe·sus fac·tor
/ ˈrēsəs/
(abbr.: Rh fac·tor)
•
n. [in sing.]
an antigen occurring on the red blood cells of many humans (around 85 percent) and some other primates. It is particularly important as a cause of hemolytic disease of the newborn and of incompatibility in blood transfusions.

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rhesus factor

rhesus factor an antigen occurring on the red blood cells of many humans (around 85 per cent) and some other primates. It is particularly important as a cause of haemolytic disease of the newborn and of incompatibility in blood transfusions. It was named in the 1940s for the rhesus monkey in which the antigen was first observed.

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